The flags of member nations fly outside the General Assembly building at the United Nations headquarters in New York. The U.N. General Assembly overwhelmingly approved the first U.N. treaty regulating the multibillion-dollar international arms trade Tuesday.

UNITED NATIONS — The U.N. General Assembly overwhelmingly approved the first U.N. treaty regulating the multibillion-dollar international arms trade, a goal sought for over a decade to try to keep illicit weapons out of the hands of terrorists, insurgent fighters and organized crime.

The resolution adopting the landmark treaty was approved by a vote of 154 to 3 with 23 abstentions. As the numbers appeared on the electronic board, loud cheers filled the assembly chamber.

“This is an historic day and a major achievement for the United Nations,” British Foreign Secretary William Hague said. “The world wanted this treaty and would not be thwarted by the few who sought to prevent the introduction of robust, effective and legally-binding controls on the international trade in weapons.”

What impact the treaty will have in reining in the estimated $60 billion global arms trade, however, remains to be seen.

The treaty will take effect soon after 50 countries ratify it — and a lot will depend on which countries ratify and which don’t, and how stringently it is implemented.

Britain and a small group of treaty supporters sought a vote in the 193-member world body after Iran, North Korea and Syria blocked its adoption by consensus at a negotiating conference last Thursday. The three countries voted “no” on Tuesday’s resolution while Russia and China, both major arms exporters, abstained.

Many countries, including the United States, which voted for the treaty, control arms exports. But there has never been an international treaty regulating the global arms trade.

Australian Ambassador Peter Woolcott, who chaired the negotiations, said the treaty will “make an important difference by reducing human suffering and saving lives.”

“We owe it to those millions — often the most vulnerable in society — whose lives have been overshadowed by the irresponsible and illicit international trade in arms,” he told the assembly just before the vote.

But the three treaty opponents and many countries that abstained complained that the treaty has too many loopholes and can be easily “politicized.” Their key arguments include that the treaty favors exporters like the United States over importers who need arms for self-defense and doesn’t include a provision banning sales to armed groups.

The treaty will not control the domestic use of weapons in any country, but it will require countries that ratify it to establish national regulations to control the transfer of conventional arms, parts and components and to regulate arms brokers.

It covers battle tanks, armored combat vehicles, large-caliber artillery systems, combat aircraft, attack helicopters, warships, missiles and missile launchers, and small arms and light weapons. A phrase stating that this list was “at a minimum” was dropped, according to diplomats, at the insistence of the United States. Supporters complained that this limited the treaty’s scope.

The treaty prohibits states that ratify it from transferring conventional weapons if they violate arms embargoes or if they promote acts of genocide, crimes against humanity or war crimes. It also prohibits the export of conventional arms if they could be used in attacks on civilians or civilian buildings such as schools and hospitals.

In considering whether to authorize the export of arms, the treaty says a country must evaluate whether the weapon would be used to violate international human rights or humanitarian laws or be used by terrorists or organized crime. They must also determine whether the weapons transfer would contribute to or undermine peace and security.

The treaty also requires parties to the treaty to take measures to prevent the diversion of conventional weapons to the illicit market.

Ammunition was been a key issue in negotiations, with some countries pressing for the same controls on ammunition sales as arms, but the U.S. and others opposed such tough restrictions.

The final text calls for each country that ratifies the treaty to establish regulations for the export of ammunition “fired, launched or delivered” by the weapons covered by the convention.

The United Nations by long tradition has required treaties and final documents for major conferences to be adopted by consensus, though there have been exceptions. The United States insisted on consensus approval for an Arms Trade Treaty.

Hopes of reaching agreement were dashed last July when the U.S. said it needed more time to consider the proposed accord — a move quickly backed by Russia and China. In December, the General Assembly decided to hold a final conference and set last Thursday as the deadline for agreement.

This time, the United States supported the final text, but Iran, North Korea and Syria used the U.S. consensus requirement to block adoption of the treaty. There was a provision, however, that enabled U.N. members to go to the assembly for a vote if consensus wasn’t reached.